In addition to direct effects such as short circuits and submergence, extreme precipitation can cause secondary hazards like river floods, snow avalanches, and landslides.

A study published by researchers at Freie Universität Berlin’s Institute of Meteorology suggests that the areas affected by heavy precipitation may become larger in many European regions. This can have consequences for infrastructure networks; larger-scale events may damage more portions of infrastructure at the same time, and more personnel may be needed for repairs and emergency services. In addition, larger events are more likely to cause river flooding.

Rain events with 10-year return period

Future changes in frequency, size, duration, and severity of heavy precipitation events in different parts of Europe were estimated from simulations with a large number of climate models for an intermediate and high-end scenario of climate change. The study focused on rain events with a current 10-year return period of occurrence: from interviews with infrastructure providers, emergency rescue services, and private weather services it was concluded that the 10-year return period of rain events is an appropriate threshold for relevance. Changes were studied for future time-slices 2021-2050 and 2071-2100 compared with 1971-2000 as a reference.

More frequent, larger, and possibly more intense

According to the study, all over Europe the frequency of sub-daily (lasting for three hours), daily (24 hours), and multi-day (48-72 hours) heavy precipitation events will increase this century. Projected increase is highest for sub-daily events: in the high-end scenario of climate change the frequency of heavy precipitation events may increase from once every 10 years by more than 300 per cent to once every two to three years. For most of Europe, the frequency of daily and multi-day heavy precipitation events is projected to increase by up to 150 per cent; an exception is the western Mediterranean region where the number of daily and multi-day events seems to decrease.

Regions with highest increase

Currently, the frequency of heavy precipitation is highest over (parts of) Iceland, western Norway, the Alps, north-western Spain, and the Mediterranean coast, for both sub-daily, daily, and multi-day events. Except for the Mediterranean coast, these are also the regions where the projected increase of heavy precipitation is highest: the westward-facing sides of the European coasts (western Scandinavia, western Ireland, western Scotland, Iceland, and the western Balkans). Under a high-end scenario of climate change, for these regions daily and multi-day heavy precipitation events with a 10-year return period may become twice as likely, and sub-daily events even three times as likely by the end of this century, for all seasons.

The simulated changes for 2100 for a moderate scenario of climate change are 60 per cent (daily and multi-day events) to 75 per cent (sub-daily events) of the changes projected under the high-end scenario.

The article first appeared on Climate Change Post and is a digest of a scientific paper by Nissen and Ulbrich, 2017. Natural Hazards Earth System Sciences 17: 1177-1190.